Laminated stator core for dynamoelectric machines

ABSTRACT

A stator core for an induction-run motor comprises identical laminations. Each has a circular inner edge to which winding slots open. The outer edge is asymmetrical, defined by arcuate portions curved on a uniform radius concentric to the inner edge, peripherally alternating with straight portions that are parallel to mutually perpendicular lines through the center of the inner edge. Along the stator the laminations have different angular orientations, but orientations differ by uniform angular increments and preferably vary in a regular sequence along the core; hence the core as a whole is symmetrical.

United States Patent [191 Widstrand 1 Jan. 1,1974

[ LAMINATED STATOR CORE FOR DYNAMOELECTRIC MACHINES [75] Inventor: JohnC. Widstrand, Wausau, Wis.

[73] Assignee: Marathon Electric Manufacturing Corporation, Wausau, Wis.

[22] Filed: Oct. 6, 1972 [2]] Appl. No.: 295,706

[52] U.S. Cl. 310/216, 310/254 [51] Int. Cl. [102k 1/16 [58]FieldofSearch ..310/216218,254,258,

[56] References Cited UNITED STATES PATENTS 3,671,790 6/1972 Widstrand310/216 1,158,495 11/1915 Hellmund 310/258 X 2,818,515 12/1957 Dolenc310/217 X 1,173,089 2/1916 Bergman 310/259 1,882,487 10/1932 DuPont310/217 X FOREIGN PATENTS OR APPLICATIONS 1,212,622 3/1966 Germany.....3l0/2l7 469,436 7/1937 Great Britain ..3lO/258 Primary Examiner-D.F. Duggan An0rney1ra Milton Jones [5 7 ABSTRACT A stator core for aninduction-run motor comprises identical laminations. Each has a circularinner edge to which winding slots open. The outer edge is asymmetrical,defined by arcuate portions curved on a uniform radius concentric to theinner edge, peripherally alternating with straight portions that areparallel to mutually perpendicular lines through the center of the inneredge. Along the stator the laminations have different angularorientations, but orientations differ by uniform angular increments andpreferably vary in a regular sequence along the core; hence the core asa whole is symmetrical.

6 Claims, 6 Drawing Figures PATENTEUJAH 1 m4 v I 3.783.318

I sum 20? 4 PATENTEDJAN 1 I974 3.783.318

sum 30? 4 LAMINATED STATOK CORE FOR DYNAMOELECTRIC MACHINES Thisinvention relates to the stator cores of dynamoelectric machines, andmore particularly to laminated stator cores upon which the windings ofinduction-run motors are wound.

While the present invention is not limited in its applicability toinduction-run motors, nor, indeed, to motors, as distinct from otherdynamoelectric machines, the invention is herein discussed and describedwith particular reference to induction-run motors.

Conventionally the stator cores of induction-run motors are built upfrom identical laminations punched out of sheet-like stock. The cost ofthe core obviously includes not only the cost of those portions of thelamination stock that go into the laminations themselves, but also thecost of those other portions of it that must be discarded as wastetrimmings.

Where a multiplicity of identical units are to be punched or stampedfrom sheet stock, best economy of material is obtained if the units aremade as nearly square or rectangular as possible. The stator core of amotor, however, tends to be cylindrical; hence stator laminations haveordinarily been circular or near circular in outline, and theirproduction has heretofore entailed a substantial amount of scrapmaterial. To some extent waste could be minimized by using sheet stockhaving a width equal to several times the lamination diameter, andpunching the laminations out of the stock in a nested or honeycomb-likepattern. However this required a very expensive multiple or nested die,the cost of which could be justified only by material savings achievedover a long production run.

With these considerations in mind, it is a general object of the presentinvention to provide a stator core for induction motors and the like,which core comprises a stack of identical laminations that can beeconomically punched or otherwise formed out of conventional laminationstock with the use of a single progressive die and with minimumwastage'of the material, without however requiring any sacrifice ofeconomy or efficiency in other steps in the manufacture of the motorcomprising such laminations, and also without the slightest sacrifice ofany desirable characteristic of the finished motor itself.

US. Pat. No. 3,671,790 discloses a two-pole induction-run motor havingstator core laminations which are generally rectangular in outline, butwith rounded corners. The laminations for that motor can be made with aminimum of scrap, but the stator core into which they are assembledaccording to the teachings of that patent is somewhat conventional,being intended for a motor that has an unusually low shaft height and anunusually low overall height in relation to the power it develops. Whileremarkably efficient for its size and shape, the motor of that patentnevertheless involves at least a small sacrifice of performance andrequires some care in design to avoid more than a negligible sacrificeof efficiency, inasmuch as its stator core is asymmetrical relative to ahorizontal plane that contains the equator between its running poles.Specifically, having regard to one of the identical substantiallyrectangular laminations that are stacked to provide the stator core ofthat motor, the longer straight sides of that lamination are at itsbottom and its top, and the bottom one is closer to the rotor axis thanthe top one, so that the bottom running pole comprises substantiallyless core metal than the top one. In thus achieving low shaft height, amotor having such stator core laminations presents the problem that thebottom portion'of its core is subject to high magnetic densities andhence to possible magnetic saturation. As explained in the patent, thewindings for the two-running poles can be different, to accommodate thedifferent volumes of core metal that they embrace, but this implies thatspecial attention be given to the bottom windings. Thus the particularmotor of that patent, notwithstanding the relatively low cost of itsindividual stator core laminations, is not competitive on acost-per-horsepower basis with general utility motors that do notrequire unusually low shaft height.

Another object of the present invention is to provide a moreconventional motor than that of the above mentioned patent, having astator core which is symmetrical to all planes lying on the rotor axis,and therefore having symmetrical running poles as well as being adaptedfor running pole windings which present no special design problems,which more conventional motor nevertheless has its stator core made upof the asymmetrical laminations of that low shaft height motor, thusenabling one and the same inexpensive lamination to be used for the coreof either type of motor so that cost benefits accrue to both.

In short, therefore, it can be said to be anotherobject of thisinvention to impart versatility to the stator core lamination disclosedin U.S. Pat. No. 3,671,790, so that it can be. incorporated into tworather unlike types of motors.

Another object of this invention is to provide a stator core that isrelatively inexpensive by reason of the fact that its componentlaminations have straight outer edge portions and are asymmetrical, butwhich stator core can nevertheless have a generally cylindrical outersurface that is concentric to its axis.

The last stated object of the invention is of importance with respect tomotors having a conventional cy lindrical frame or shell that surroundsthe stator core. The frame serves to pilot the end bells of the motor,in which the shaft bearings are secured. If the stator core isasymmetrical, or departs too greatly from having a fully cylindricalexterior surface (i.e., has excessive flat areas), it tends to force theframe out of round when it is inserted into the frame, with the resultthat the frame cannot properly cooperate with the end bells to assureconcentricity of the bearings.

Thus it can be said to be another object of this invention to provide astator core comprised of a stack of identical laminations that can bemade economically by reason of the fact that they are individuallyasymmetrical, with straight edge portions, but which stator corenevertheless has no tendency to force a cylindrical motor frameout-of-round when it is inserted into the frame, to avoid problems insecuring end bells to the frame with their shaft bearings in concentricrelation.

Still another object of this invention is to provide a laminated statorcore which is lower in cost than heretofore conventional equivalentstator cores, and which in no wise impairs the quality of the motor thatincorporates it but may in many cases afford advantages with respect tomotor cooling.

Another object of this invention is to achieve overall cost savings inthe production of induction-run motors and similar machines by reason ofreducing the amount of metal in their stator cores without any sacrificein performance, and thereby effecting economies not only in the materialcomprising the motor cores but also in the heat treating equipmentneeded for processing core laminations at a given rate, and even in costof shipping the finished motors by reason of their somewhat reducedweight.

With these observations and objectives in mind, the manner in which theinvention achieves its purpose will be appreciated from the followingdescription and the accompanying drawings, which exemplify theinvention, it being understood that changes may be made in the specificapparatus disclosed herein without departing from the essentials of theinvention set forth in the appended claims.

The accompanying drawings illustrate several complete examples ofembodiments of the invention constructed according to the best modes sofar devised for the practical application of the principles thereof, andin which:

FIG. 1 is an end view of a stator core embodying the principles of thisinvention;

FIG. 2 is a view in side elevation of the stator core shown in FIG. 1;

FIGS. 3 6 are end views of variously modified forms of stator coresembodying the invention.

Referring now to the accompanying drawings, and particularly to theembodiment of the invention disclosed in FIGS. 1 and 2, a stator coreembodying the principles of this invention comprises a stack oflaminations 6, all of them identical with the laminations disclosed inthe above mentioned U.S. Pat. No. 3,671,790. Thus each lamination issubstantially octagonal in outline and has an opening 8 that is definedby a circular inner edge 9. In the stack that comprises the core 5, thecircular edges 9 of the several laminations are concentric with oneanother to define a bore in which a rotor (not shown) is received. Thecenter of the circular edge 9 in each lamination of course coincideswith the rotor axis.

At circumferentially spaced intervals the circular edge 9 is interruptedby inwardly opening slots 10 and 10', as is conventional in inductionmotor stator core laminations. In the core stack these slots registerwith one another to provide grooves 11 in which stator windings (notshown) are received. The slots in each lamination are arrangedsymmetrically to a pair of mutually perpendicular lines 12 and 13 whichintersect at the center of the circular edge 9. In the assembled corethe lines 12 for the several laminations define an equatorial planebetween a pair of running poles, and the lines 13 define an equatorialplane between starting poles. As shown, three slots, designated 10, areequispaced to opposite sides of the line'12 and are symmetrical to theline 13, which slots are of lesser depth than the remaining slots 10'since they receive only starting windings. The larger slots 10, whichare equispaced from the line 13 and symmetrical to the line 12,accommodate both running and starting windings. Further detailsconcerning the arrangement of the respective windings relative to theseveral slots, and the poles defined by the windings, can be obtainedfrom the above mentioned U.S. Pat. No. 3,671,790.

The generally octagonal outline of each lamination is defined bystraight edge portions 17, 18 and 19 alternating around its peripherywith arcuately curved edge portions 14 and 15. The arcuate edge portions14 and 15 are all curved on a uniform radius concentric to the circularinner edge 9, and it will be noted that these arcuate edge portions areof somewhat lesser circumferential extent than any of the straight edgeportions, so that the outline of the lamination could be regarded as arectangle with clipped or rounded corners.

The lamination has two longer straight edge portions 17 and 18 which areparallel to the line 12, and two shorter straight edge portions 19 whichare parallel to the line 13. The shorter straight edges 19 areequidistant from the reference line 13, and the lamination issymmetrical to that line; but it is asymmetrical to the line 12 in thatthe long straight edge 17 is farther from that line than its oppositeedge 18. In consequence, the straight edge 18 is longer than itsopposite straight edge 17, and the arcuate edge portions 15 that areadjacent to the longest straight edge 18 are of somewhat lessercircumferential extent than the other two arcuate edge portions 14.

Nevertheless, the stator core 5 that is formed from such laminations issymmetrical to both of the planes defined by the lines 12 and 13 byreason of the fact that half of the laminations in the core have theirlongest straight edges 18 at one side of the core, while the other halfof the laminations have their corresponding straight edge portions atthe diametrically opposite side of the core, and the differentlyoriented laminations alternate axially along the core in a regularsequence. This is to say that in the core certain of the laminationshave their straight edges 18 adjacent to the straight edges 17 of otherlaminations.

As shown in FIG. 2, the laminations are arranged in the core in groups,each group containing the same number of flatwise contiguous laminationsas all the other groups, with all of the laminations in each groupidentically oriented; and the laminations of each group are oriented atto the laminations of its adjacent groups. Obviously the laminationscould be stacked with every lamination oriented oppositely to itsflatwise contiguous laminations.

Because the winding slots 10 and 10' in the laminations are symmetricalto the planes defined by lines 12 and 13, those slots define perfectlystraight and regular winding grooves 11 in the core, notwithstanding thedifferent orientations of the laminations along the core. The windinggrooves are thus well adapted to accommodate symmetrical windings.

As a result of the described arrangement of the laminations in the core,the external surface of the core has circumferentially extendingflat-bottomed grooves 21 therein. However, these grooves are at uniformintervals around and along the core and are symmetrical to the planesdefined by the lines 12 and 13; hence the core metal is in all respectssymmetrical to the motor poles. Furthermore, despite the saving inlamination stock that is effected by reason of the edge portion 18 ofeach lamination being straight and relatively close to the circularinner edge 9, there is adequate metal all around the core to avoid zonesof high magnetic density. In effect, where a straight edge portion onone lamination may tend to create a zone of magnetic saturation, theexcess flux simply moves over into neighboring differently orientedlaminations.

Note, too, that by reason of the lamination arrangement, the curvedexterior surface portions of the core, considered as a whole, have agreater circumferential extent than the arcuate edge portions of anindividual lamination. In other words, the exterior surface of the coremore nearly approaches a cylinder than the outline of an individuallamination approaches a circle. Hence the economy of lamination materialachieved by the nearly rectangular configuration of the individuallaminations does not result in a correspondingly great tendency to causeout-of-roundness of a motor frame into which the core is inserted.

The grooves 21 that appear in the external surface of the core tend toimprove motor performance by promoting better cooling than would beattainable without them. In drip-proof motors with frames and straightthrough cooling, the grooves 21 make for better cooling by reasonv ofthe greater exposure of lamination area to cooling air; and intotallyenclosed motors the grooves 21 enhance cooling effect byaffording more effective distribution ofcontact area between the statorcore and the framefand by defining increased heat radiation andconvection areas on the core.

FIG. 3 illustrates a core 5' which provides slightly better rounding outof a rolled steel frame than the core of FIGS. 1 and 2. Like the latter,the core 5 of FIG. 3 is comprised of identical laminations6, each havingan opening 8 defined by a circular inner edge 9, with equispaced slots10 opening inwardly thereto. In this case the winding slots are all ofthe same size, but, as is usually the case in conventional induction-runmachines, they arearranged symmetrically to mutually perpendicular lines12 and 13 through the center of the opening, which lines define theequatorial planes between the poles of the motor.

The core 5 is generally similar to the core 5, too, in that each of itslaminations 6' has a more or less octangonal outline defined by straightedge portions 17 18, 19 and 20', alternating around the periphery witharcuate edge portions 14', 15' and 16 that are curved on a uniformradius about the center of the inner edge 9. However, as compared withthe above described lamination 6, the arcuate outer edge portions of thelamination 6" have, in total, a somewhat greater circumferential extent;the straight edge portions 17 more nearly define a square than arectangle; and the lamination 6 is asymmetrical to both of the referencelines 12 an'd'13; Specifically, of the opposite straight edge portionsl7"and 18" that are parallel to the line 12, the

' edge 18-is closer to the line 12 (and hence longer) than edge 17'; andthe straight edge portion 19, which parallels the line 13, is closer tothat line (hence longer) than its opposite straight edge 20. However,the two longer straight edges 18 and 19' are preferably of equal length,as are the two shorter straight edges 17' and 20'. The two oppositearcuate edge portions 16 that extend between longer and shorter straightedges are of equal circumferential extent; the arcuate edge 15 thatconnects the two longer straight edges is of lesser circumferentialextent; and its opposite arcuate edge 14 has the greatestcircumferential extent. The line of symmetry is at 45 to the referencelines 12 and 13 and extends through arcuate edges 14' and 15'. (Notethat in all instances the term symmetry is used herein to denotemirror-image or flipped symmetry as well as true symmetry.) 7

, As in the FIGS. 1 and 2 embodiment, the laminations 6' are arranged inthe core 5' in a regularly alternating sequence, with half of thelaminations of the core shown oriented 180 from the other half. However,it will be'apparent that the angular orientations of the severallaminations could be varied in many different ways. For example, eachlamination could be displaced rotationally by one or two slots from itsadjacent laminations since the slots are of uniform size and uniformlyspaced.

Where core laminations are vheld assembled by through bolts 30 passingthrough holes in the laminations, the bolt-receiving holes must ofcourse be arranged symmetrically to the equatorial lines 12 and 13, aswith the bolt receiving holes 31 in FIG. 1. In such cases thearrangement of the bolt receiving holes requires'laminations tobe'oriented at either or to one another. A wider variety of orientationsis possible where laminations are secured together by welding.

' In most cases, for every lamination (or nearly every lamination) thatis oriented in one direction, there will be another that is at 180 toit; and in all cases the sequence in which the orientation oflaminations isvaried along the stack is preferably a regular one, toprovide overall symmetry of the core.

Because of the four straight edge portions on the lamination 6',arranged in a nearly square configuration, such laminations can bepunched out of lamination stock with very little waste material, yet thecore that they cooperate to form has an overall exterior surfacedefining a substantially large portion of a full cylinder and thus haslittle tendency to impart out-of-roundness to a rolled steel frame intowhich it is inserted, as well as providing symmetrical motor poles withno magnetic constriction. It will be apparent that the external surfaceof the core 5' defined by the laminations 6' will have regularlydistributed flat-bottomed grooves that are generally similar tothegrooves 21 previously described, and which will afford the same motorcooling advantages.

The core 5" that is illustrated in FIG. 4, which comprises a stack ofidentical laminations 6" of further modified form, has a full and truecylindrical exterior surface overall, interrupted, however, byflat-bottomed grooves at regular intervals aroundand along it,corresponding to the grooves 21 previously described. The core 54" willthus afford complete assurance that roundness will be maintained in aframe into which it is inserted, will have the motor cooling advantagesmentioned above, and will at the same time be lower in cost than a coremade of heretofore conventional round laminations, owing to savings inlamination material scrap.

As with the laminations previously described, each of the laminations 6"has an opening 8 defined by a circular inner edge 9, with slots 10 thatopen inwardly thereto, arrangedsymmetrically to mutually perpendicularlines 12 and 13 that intersect at the center of the inner edge. Andagain, each lamination 6" hasan outer edge consisting of straight edgeportions 17" and 19 which alternate circumferentially with arcuate edgeportions 14" and 15" that are curved on a uniform radius concentric tothe inner edge. In this case, however, there are only two straight edgeportions one of them (designated 17") parallel to the line 12, the other(19") parallel to the line 13; and likewise there are only two arcuateedge portions. Preferably the two straight edge portions are at equaldistances from the center of the inner edge 9, so that a line ofsymmetry at 45 to the lines 12 and 13 extends through said center andthrough both arcuate edge portions.

In this case, again, half of the laminations 6 in the core are shownoriented at 180 to the other half of the laminations, but other schemesof varying the lamination orientation along the core can be used, asexplained above.

FIG. 5 illustrates a core comprising identical laminations, each havingan arrangement of small and large slots and 10 like that of thelaminations of FIG. 1, but having an outside edge somewhat similar tothat on the laminations of FIG. 4. The FIG. 5 laminations differ fromthose of FIG. 4 in that each of the FIG. 5 laminations has one of itsstraight outer edge portions 17" closer to the center of its circularinner edge than its other straight edge portion 19', thus taking fulladvantage of the lesser depth of the upper slots 10. The laminations ofthe FIG. 5 embodiment vary in their orientations along the stator in themanner described in connection with FIGS. 1 and 2.

FIG. 6 illustrates an embodiment of the invention in which eachlamination has three straight outer edge portions, two of whichdesignated by 17" are at opposite sides of the lamination and parallelto the equatorial line 12 and the third of which designated 19" isperpendicular to the other two. All three straight edge portions are atthe same distance from the center of the inner circular edge 9. In thiscase the stator is shown as having 32 winding slots, to provide afour-pole induction run motor, including a pair of smaller slots 10 ineach quadrant, with the two slots of each such pair on opposite sides ofone of the equatorial lines 12 and R3. The straight edge portions arerelatively close to the center of the inner edge, to take full advantageof the small slots and achieve maximum economy of lamination stock.

In this case the laminations along the length of the stator have fourdifferent orientations, and the different orientations differ from oneanother by multiples of 90. It will be apparent that generally the samelamination configuration and orientation arrangement could be used ifall winding slots were of the same size.

From the foregoing description taken with the accompanying drawings itwill be apparent that the present invention provides a stator core forinduction-run motors and similar dynamoelectric machines, which core iscompletely symmetrical to all planes lying on its axis and hassufficient cylindrical surface area to assure maintenance of roundnessof a frame into which it is inserted, but which core is neverthelesscomprised of laminations that are asymmetrical and have straight outeredge portions so that they can be made with less waste of laminationstock than heretofore conventional symmetrical laminations.

Those skilled in the art will appreciate that the invention can beembodied in forms other than as herein disclosed for purposes ofillustration.

The invention is defined by the following claims:

1. A stator core for a dynamoelectric machine, having slots which openradially inwardly to a circular bore and in which windings can bereceived to produce a pair of starting poles and a pair of runningpoles, the poles of each pair being disposed at opposite sides of one ofa pair of mutually perpendicular diametral planes that lie on the axisof the bore, said core comprising flatwise superimposed laminations, andthe laminations being characterized by:

A. each lamination having 1. a substantially circular inner edge,

2. circumferentially spaced slots of two different radial depths openingto the inner edge, the slots of each depth being arranged in two likegroups of circumferentially adjacent slots,

a. the two groups of slots of smaller depth being at opposite sides ofone of a pair of mutually perpendicular straight lines through thecenter of the inner edge,

b. the two groups of slots of larger depth being at opposite sides ofthe other of said lines, and

c. the two groups of slots of each depth being arranged symmetrically toboth of said lines, and

3. the outer edge of each lamination having straight portions which areparallel to said lines and which peripherally alternate with arcuateportions curved on a uniform radius about said center, a straightportion parallel to said one line being closer to said center than anystraight portion parallel to said other line and also being closer tosaid center than its diametrically opposite outer edge portion so thatthe lamination is asymmetrical about at least said one line; and

B. said laminations being flatwise stacked in the core with theircircular inner edges concentric and with substantially half of thelaminations oriented at 89 tsx epths hal the Orientations o the ainations along the stack varying in a regular sequence.

2. The annular core of claim 1, further characterized by:

the outer edge of each lamination further having 1. a second straightportion parallel to said one straight portion and at the opposite sideof said one line but spaced a farther distance therefrom, and

2. further straight portions at both sides of the other of said linesand parallel thereto, both of said further straight portions beingspaced a greater distance from said center than either of said first andsecond straight portions.

3. A laminated substantially annular core for a dynamoelectric machine,having winding slots that open to its inner circumference at spacedintervals therearound, said stator core being characterized by:

A. substantially all of the laminations that comprise the core beingidentical, and each having 1. a substantially circular inner edge,

2. circumferentially spaced slots opening to said inner edge andarranged symmetrically to a pair of mutually perpendicular lines throughthe center of said inner edge, and

3. an outer edge having straight portions peripherally alternating witharcuate portions curved on a uniform radius about said center, therebeing at least one straight portion parallel to each of said lines andeach of said straight portions having a point at its middle that iscloser to the line it parallels than the point on the outer edge that isdiametrically opposite it, so that the lamination is asymmetrical aboutboth of said lines; and

B. said laminations being flatwise stacked in the core with theircircular inner edges concentric and with substantially half of thelaminations oriented at to the other half, the orientations of thelaminations along th stack varying in a regular sequence.

radial depths opening to the inner edge, said slots being arranged inlike groups of circumferentially adjacent like slots, there being agroup of smaller depth slots at each side of a line through the centerof said inner edge and the groups of like slots being arrangedsymmetrically to said line and to another line that is perpendicular tosaid one line and extends through said center,

. the outer edge of each lamination having straight portions which areparallel to said lines and which peripherally alternate with arcuateportions curved on a uniform radius about said center,

a. there being two straight portions parallel to the other of said linesand at opposite sides thereof, and

b. there being at least one other straight portion parallel to the firstmentioned line and which is closer to said center than its diametricallyopposite outer edge portion so that the lamination is asymmetrical aboutsaid one straight line; and

B. substantially every lamination in the core being oriented edgewiserotationally at to one other lamination so that there is a substantiallyequal number of laminations at each such orientation.

5. The stator core of claim 4, further characterized the outer edgeportion of each lamination that is diametrically opposite said at leastone other straight portion being straight and parallel to said one lineand spaced at a greater distance therefrom than said at least one otherstraight portion but at a lesser distance therefrom than the spacing ofsaid two straight portions from said other line.

6. The stator core of claim 4, further characterized a. each laminationhaving four groups of slots of each depth, each group of smaller depthslots being centered on one of said lines, and

b. the outer edge portion of each lamination that is diametricallyopposite said at least one other straight portion being arcuate.

1. A stator core for a dynamoelectric machine, having slots which openradially inwardly to a circular bore and in which windings can bereceived to produce a pair of starting poles and a pair of runningpoles, the poles of each pair being disposed at opposite sides of one ofa pair of mutually perpendicular diametral planes that lie on the axisof the bore, said core comprising flatwise superimposed laminations, andthe laminations being characterized by: A. each lamination having
 1. asubstantially circular inner edge,
 2. circumferentially spaced slots oftwo different radial depths opening to the inner edge, the slots of eachdepth being arranged in two like groups of circumferentially adjacentslots, a. the two groups of slots of smaller depth being at oppositesides of one of a pair of mutually perpendicular straight lines throughthe center of the inner edge, b. the two groups of slots of larger depthbeing at opposite sides of the other of said lines, and c. the twogroups of slots of each depth being arranged symmetrically to both ofsaid lines, and
 3. the outer edge of each lamination having straightportions which are parallel to said lines and which peripherallyalternate with arcuate portions curved on a uniform radius about saidcenter, a straight portion parallel to said one line being closer tosaid center than any straight portion parallel to said other line andalso being closer to said center than its diametrically opposite outeredge portion so that the lamination is asymmetrical about at least saidone line; and B. said laminations being flatwise stacked in the corewith their circular inner edges concentric and with substantially halfof the laminations oriented at 180* to the other half, the orientationsof the laminations along the stack varying in a regular sequence.
 2. Theannular core of claim 1, further characterized by: the outer edge ofeach lamination further having
 2. further straight portions at bothsides of the other of said lines and parallel thereto, both of saidfurther straight portions being spaced a greater distance from saidcenter than either of said first and second straight portions. 2.circumferentially spaced slots opening to said inner edge and arrangedsymmetrically to a pair of mutually perpendicular lines through thecenter of said inner edge, and
 2. circumferentially spaced slots of twodifferent radial depths opening to the inner edge, the slots of eachdepth being arranged in two like groups of circumferentially adjacentslots, a. the two groups of slots of smaller depth being at oppositesides of one of a pair of mutually perpendicular straight lines throughthe center of the inner edge, b. the two groups of slots of larger depthbeing at opposite sides of the other of said lines, and c. the twogroups of slots of each depth being arranged symmetrically to both ofsaid lines, and
 2. circumferentially spaced slots of two differentradial depths opening to the inner edge, said slots being arranged inlike groups of circumferentially adjacent like slots, there being agroup of smaller depth slots at each side of a line through the centerof said inner edge and the groups of like slots being arrangedsymmetrically to said line and to another line that is perpendicular tosaid one line and extends through said center,
 3. an outer edge havingstraight portions peripherally alternating with arcuate portions curvedon a uniform radius about said center, there being at least one straightportion parallel to each of said lines and each of said straightportions having a point at its middle that is closer to the line itparallels than the point on the outer edge that is diametricallyopposite it, so that the lamination is asymmetrical about both of saidlines; and B. said laminations being flatwise stacked in the core withtheir circular inner edges concentric and with substantially half of thelaminations oriented at 180* to the other half, the orientations of thelaminations along the stack varying in a regular sequence.
 3. the outeredge of each lamination having straight portions which are parallel tosaid lines and which peripherally alternate with arcuate portions curvedon a uniform radius about said center, a straight portion parallel tosaid one line being closer to said center than any straight portionparallel to said other line and also being closer to said center thanits diametrically opposite outer edge portion so that the lamination isasymmetrical about at least said one line; and B. said laminations beingflatwise stacked in the core with their circular inner edges concentricand with substantially half of the laminations oriented at 180* to theother half, the orientations of the laminations along the stack varyingin a regular sequence.
 3. A laminated substantially annular core for adynamoelectric machine, having winding slots that open to its innercircumference at spaced intervals therearound, said stator core Beingcharacterized by: A. substantially all of the laminations that comprisethe core being identical, and each having
 3. the outer edge of eachlamination having straight portions which are parallel to said lines andwhich peripherally alternate with arcuate portions curved on a uniformradius about said center, a. there being two straight portions parallelto the other of said lines and at opposite sides thereof, and b. therebeing at least one other straight portion parallel to the firstmentioned line and which is closer to said center than its diametricallyopposite outer edge portion so that the lamination is asymmetrical aboutsaid one straight line; and B. substantially every lamination in thecore being oriented edgewise rotationally at 180* to one otherlamination so that there is a substantially equal number of laminationsat each such orientation.
 4. A stator core for a dynamoelectric machine,having slots which open radially inwardly to a circular bore and inwhich starting and running windings can be received to produce pairs ofdiametrically opposite poles, said core comprising flatwise superimposedlaminations, and the laminations being characterized by: A. eachlamination having
 5. The stator core of claim 4, further characterizedby: the outer edge portion of each lamination that is diametricallyopposite said at least one other straight portion being straight andparallel to said one line and spaced at a greater distance therefromthan said at least one other straight portion but at a lesser distancetherefrom than the spacing of said two straight portions from said otherline.
 6. The stator core of claim 4, further characterized by: a. eachlamination having four groups of slots of each depth, each group ofsmaller depth slots being centered on one of said lines, and b. theouter edge portion of each lamination that is diametrically oppositesaid at least one other straight portion being arcuate.